1. Field of the Invention
The present invention relates to a copying machine so adapted as to convey a document to illuminate and scan the surface of the document and record a copy image of the document on strip-shaped continuous copy paper such as rolled-paper.
2. Description of the Prior Art
In an electrostatic process copying machine conventionally widely used, a copy image of a document is formed on copy paper in the following manner. The document is illuminated and scanned, and a photoreceptor is exposed to reflected light from the document. Consequently, an electrostatic latent image is formed on the surface of the photoreceptor. The electrostatic latent image is developed into a toner image, and the toner image is heated and fixed to the copy paper. Therefore, the copy image of the document is formed on the copy paper.
Examples of such an electrostatic process copying machine recently provided include one capable of copying a document of large size such as 0-th of series A in Japanese Industrial Standard (hereinafter referred to as "A0 size"). "A0 size" refers to one of finished sizes of paper under Japanese Industrial Standard, that is, 841 (mm).times.1189 (mm). In a copying machine capable of copying such a document of large size, the document is illuminated and scanned by conveying the document with an optical system being fixed. On the other hand, it is difficult to handle copy paper sheets of large size such as A0 size one at a time. Accordingly, rolled-paper which is stripshaped continuous copy paper wound in a roll shape may, in some cases, be applied to the copy paper sheets.
A so-called synchro sensor for sensing a rear end of a document to sense the length of the document is provided in a document conveying path. The timing at which rolled-paper is cut is set on the basis of the timing at which the synchro sensor senses the rear end of the document, thereby to make it possible to cut the rolled-paper to lengths corresponding to the size of the document.
In the above described copying machine, when a plurality of copies are made from one document, the document is conveyed by repeatedly moving back and forth in the document conveying path. More specifically, when the document is conveyed in a forward direction which is one direction in which the document is conveyed, an image forming operation with illuminating and scanning of a document is performed. When the document is conveyed in a reverse direction which is the other direction in which the document is conveyed, the image forming operation is not performed but the document is only conveyed.
When the document is conveyed in the forward direction, the rear end of the document is sensed by the above described synchro sensor, and the timing at which the rolled-paper is cut is set each time.
In the above described construction, however, when a plurality of copies are made, the rear end of the document is sensed by the synchro sensor for each copying operation, and the timing at which the rolled-paper is cut is set on the basis of a sensing output of the synchro sensor. Accordingly, the lengths of copy paper sheets obtained by the cutting slightly vary due to a sensing error in the synchro sensor. Consequently, the lengths of the copy paper sheets each having a copy image of the document formed thereon vary, resulting in a poor appearance.